This invention relates to textile machines such as tufting machines or the like which utilize multiple yarn ends, and more particularly to a broken yarn end detector device for such machines for providing a signal when a yarn end is broken, and for stopping the machine upon such occurrence.
In machines which manipulate or utilize a multiplicity of yarn ends or strands which are fed to yarn manipulating instrumentalities, it is common for a yarn to break due to excessive tension, frictional rubbing or defects in the yarn itself. Machines of this type include tufting machines, looms, knitting machines and the like. For example, in a tufting machine where more than 1,000 needles each carrying an individual yarn is employed for penetrating a backing material to insert loops of yarn therein, when a yarn fed to a particular needle breaks, stitches are no longer formed by that needle. Knitting stitches likewise cease for a particular needle when the yarn fed to that needle breaks, and similarly if a warp or filling yarn breaks while being fed to a loom interlacing of that yarn terminates and the weave is defective.
Yarn break detectors and stop motion devices for various yarn manipulating textile machines are known in the prior art. Most of these devices utilize complicated electro-mechanical means requiring delicate positioning or adjusting which lose their sensitivity in the high lint environment of the yarn manipulating machines. Thus, they are not only difficult to adjust, but also to maintain. Prior art devices of this type include Jackson U.S. Pat. No. 3,529,560 which requires a drop wire to slide down an electrode bar which is insulated from the drop wire to engage an electrode. In Merkle U.S. Pat. No. 3,764,773 a drop wire is supported on the yarn which is carried through eyelets in a pivotable electro-magnetically controlled lever, the drop wire falling when the yarn is broken to open the circuit to the electromagnet and close a circuit to stop the machine. In other known prior art, a light beam is disposed across the machine from a transmitter to a receiver and when the beam is broken a circuit is activated to shut the machine. For example, in Jackson U.S. Pat. No. 3,687,095 a light beam is positioned so that when a yarn breaks the yarn drops into the path of the light beam to activate the circuit. In operation, however, particularly in the tufting art, the light beam is offset from the plane of the yarns and when the yarn breaks it may not fall into the path of the light beam but fall on top of another yarn, especially in high speed machines and in those machines having close gauge where the yarns are disposed closely adjacent each other. When this occurs, the broken yarn may even be pulled along by an adjacent yarn and not be noticed until a substantial amount of defective fabric has been produced. Thus, the unreliability of this arrangement has resulted in minimal use or in its non-use.
An improvement to these prior art devices is that disclosed in Beverly U.S. Pat. No. 4,522,139 in which a series of fingers are held in a raised position by respective yarns and when a yarn breaks, the finger drops into the path of the light beam to activate circuitry to stop the machine. However, because of the need for the light beam the fingers should be placed close to the needles so that the light transmitting and receiving means may be supported on a rigid portion of the machine, and thus if a yarn breaks the needle associated with that yarn almost immediately stops stitching. However, in high speed machines this can happen quickly before the circuitry is activated. Moreover, in certain tufting machines the yarn is trained about a substantial number of feed rollers and guides so that a substantial amount of tension is placed on the yarn between the rollers or guides and the needles, and thus if a yarn break occurs substantially upstream of the rollers or guides, i.e., between the creel or beam, the broken yarn will not be detected until the end of the broken strand is relatively close to the fingers.
It is therefore highly desirable to have a reliable yarn break detecting device which is not affected by the speed of the machine which can be placed a substantial distance from the needles or other yarn manipulating instrumentalities to detect a break upstream therefrom and which may be utilized by itself or in conjunction with apparatus such as that disclosed in the aforesaid Beverly patent to provide a substantially 100 percent reliable broken yarn detection system minimizing the production of defective fabric.